JP-2010-196687A shows a fuel injection apparatus in which a liquefied gas fuel (for example, dimethyl ether: DME) in a fuel tank is supplied to a high-pressure pump by a feed pump and the pressurized fuel is supplied to a fuel injector through a common-rail. The fuel injector injects the liquefied gas fuel into a cylinder of an internal combustion engine.
The high-pressure pump is provided with a plunger which reciprocates and pressurizes the liquefied gas fuel. A housing of the high-pressure pump defines a plunger chamber in which the plunger is accommodated. Further, the housing defines a fuel gallery into which the liquefied gas fuel is introduced from the fuel tank. The liquefied gas fuel in the fuel gallery is supplied to the plunger chamber. Furthermore, the high-pressure pump is provided with a solenoid valve which opens and closes a communication passage which fluidly connects the fuel gallery and the plunger chamber. When the solenoid valve is energized to attract a valve body, the communication passage is closed.
In the above fuel injection apparatus, when the plunger is at suction stroke, the liquefied gas fuel is suctioned from the fuel gallery into the plunger chamber, whereby a fuel pressure in the fuel gallery is decreased. When it is unnecessary to supply the liquefied gas fuel to a common-rail, the liquefied gas fuel in the plunger chamber is returned to the fuel gallery at discharge stroke, whereby the fuel pressure in the fuel gallery is increased. Therefore, the pressure in a fuel gallery is significantly varied which generates a pressure pulsation.
When the fuel pressure in the fuel gallery is decreased, the fuel pressure in the fuel gallery becomes lower than a vapor pressure of the liquefied gas fuel, so that the liquefied gas fuel is vaporized. It is likely that the plunger chamber is filled with the vaporized fuel and a vapor lock may occur.
Meanwhile, when the fuel pressure in the fuel gallery is increased, it is likely that the fuel pressure in a fuel gallery may exceed a pressure resistance of an O-ring which maintains the oil-tight of the fuel gallery. It is likely that the O-ring may be broken and the fuel may leak outside.